Estimation of speciated and total mercury dry deposition at monitoring locations in Eastern and Central North America

Abstract

Dry deposition of speciated mercury, i.e., gaseous oxidized mercury (GOM), particulate bound mercury (PBM), and gaseous elemental mercury (GEM), was estimated for the year 2008–2009 at 19 monitoring locations in Eastern and Central North America. Dry deposition estimates were obtained by combining monitored 2–4 hourly speciated ambient concentration with modeled hourly dry deposition velocities (<i>V</i><sub>d</sub>) calculated using forecasted meteorology. Annual dry deposition of GOM + PBM was estimated to be in the range of 0.4 to 8.1 μg m<sup>−2</sup> at these locations with GOM deposition being mostly 5 to 10 times higher than PBM deposition, due to their different <i>V</i><sub>d</sub> values. Net annual GEM dry deposition was estimated to be in the range of 5 to 26 μg m<sup>−2</sup> at 18 sites and 33 μg m<sup>−2</sup> at one site. The estimated dry deposition agrees very well with limited surrogate-surface dry deposition measurements of GOM and PBM, and also agrees with litterfall mercury measurements conducted at multiple locations in Eastern and Central North America. This study suggests that GEM contributes much more than GOM + PBM to the total dry deposition at the majority of sites considered here; the only exception is at locations close to significant point sources where GEM and GOM + PBM contribute equally to the total dry deposition. The relative magnitude of the speciated dry deposition and their good comparison with litterfall deposition suggest that mercury in litterfall primarily originates from GEM, consistent with previous limited field studies. The study also supports previous analyses suggesting that total dry deposition of mercury is equally if not more important as wet deposition of mercury on a regional scale in Eastern North America

Mercury Wet Deposition and Speciated Air Concentrations from Two Urban Sites in New York State: Temporal Patterns and Regional Context

“…The minimum detection limits for RGM and PBM of 0.46 pg/m 3 and 1.1 pg/m 3 , respectively, reported by Huang et al (2010) as three times the standard deviation of the system blanks, were used. Data from these two sites have been used in recent studies to estimate dry and total depositional Hg loadings (Zhang et al, 2012a) and evaluate predictions of speciated air concentrations from photochemical models (Baker and Bash, 2012;Zhang et al, 2012b). Although there is evidence that the Tekran instruments may underestimate ambient RGM and PBM by as much as a factor of 2-3 (e.g., Gustin et al, 2013), no attempt was made to adjust the data in any way, but we acknowledge this may be an important source of uncertainty.…”

A diagnostic evaluation of modeled mercury wet depositions in Europe using atmospheric speciated high-resolution observations

“…A recent study by Zhang et al (2012b) found that between 50 and 70% of the total mercury deposition is due to GOM and PBM, although these species make up only 1% of the total gaseous mercury (TGM). GEM plays only a role for dry deposition and it needs to be considered that depending on the surface type about half of the deposited GEM is quickly re-emitted into the atmosphere (Zhang et al, 2012a). On annual average water bodies and soils can even release more GEM than is deposited, depending on deposition in the past (Bash, 2010).…”

Diurnal and seasonal variability in size-dependent atmospheric deposition fluxes of polycyclic aromatic hydrocarbons in an urban center

“…Model parameters for the 'Urban' land use category were used here since the measurement site is within an urban area. Detailed description of the model and related parameters can be found in Zhang et al (2001) with modifications described by Zhang et al (2012). On-site meteorological data were not measured.…”